Cards

Cards are a common organizing unit for modern user interfaces (UI). At their core, they’re just rectangular containers with borders and padding. However, when utilized properly to group related information, they help users better digest, engage, and navigate through content. This is why most successful dashboard/UI frameworks make cards a core feature of their component library. This article provides an overview of the API that bslib provides to create Bootstrap cards.

Setup code

To demonstrate that bslib cards work outside of Shiny (i.e., in R Markdown, static HTML, etc), we’ll make repeated use of statically rendered htmlwidgets like plotly and leaflet. Here’s some code to create those widgets:

library(bslib)
library(shiny)
library(htmltools)
library(plotly)
library(leaflet)

plotly_widget <- plot_ly(x = diamonds$cut) %>%
  config(displayModeBar = FALSE) %>%
  layout(margin = list(t = 0, b = 0, l = 0, r = 0))

leaflet_widget <- leafletOptions(attributionControl = FALSE) %>%
  leaflet(options = .) %>%
  addTiles()

Shiny usage

Cards work equally well in Shiny. In the examples below, replace plotly_widget with plotlyOutput() and leaflet_widget with leafletOutput() to adapt them for Shiny server-rendered plots/maps.

Hello card()

A card() is designed to handle any number of “known” card items (e.g., card_header(), card_body(), etc) as unnamed arguments (i.e., children). As we’ll see shortly, card() also has some useful named arguments (e.g., full_screen, height, etc).

At their core, card() and card items are just an HTML div() with a special Bootstrap class, so you can use Bootstrap’s utility classes to customize things like colors, text, borders, etc.

card(
  card_header(
    class = "bg-dark",
    "A header"
  ),
  card_body(
    markdown("Some text with a [link](https://github.com)")
  )
)

A header

Some text with a link

Implicit card_body()

If you find yourself using card_body() without changing any of its defaults, consider dropping it altogether since any direct children of card() that aren’t “known” card() items, are wrapped together into an implicit card_body() call.¹ For example, the code to the right generates HTML that is identical to the previous example:

card(
  card_header(
    class = "bg-dark",
    "A header"
  ),
  markdown("Some text with a [link](https://github.com).")
)

A header

Some text with a link.

Restricting growth

By default, a card()’s size grows to accommodate the size of it’s contents. Thus, if a card_body() contains a large amount of text, tables, etc., you may want to specify a height or max_height. That said, when laying out multiple cards, it’s likely best not to specify height on the card(), and instead, let the layout determine the height layout_column_wrap().

Although scrolling is convenient for reducing the amount of space required to park lots of content, it can also be a nuisance to the user. To help reduce the need for scrolling, consider pairing scrolling with full_screen = TRUE (which adds an icon to expand the card’s size to the browser window). Notice how, when the card is expanded to full-screen, max_height/height won’t effect the full-screen size of the card.

card(
  max_height = 250,
  full_screen = TRUE,
  card_header(
    "A long, scrolling, description"
  ),
  lorem::ipsum(paragraphs = 3, sentences = 5)
)

A long, scrolling, description

Consectetur condimentum erat rhoncus class? In curae porta ac, euismod semper enim dictum vulputate. Metus pellentesque sed netus mauris eget lobortis praesent praesent auctor ac sed nunc! Sagittis eros viverra imperdiet, eu senectus nec tincidunt fusce, montes semper. Sociis ornare.

Consectetur potenti orci semper phasellus lacus integer, nascetur, curabitur commodo, sociis penatibus luctus. Diam habitant egestas, tortor nisl, aliquet viverra facilisi iaculis natoque. Condimentum gravida suspendisse: iaculis et fames tempor. Nam proin montes penatibus aptent, urna ultricies tortor pulvinar suscipit! Mi risus euismod sociis: dictumst facilisi massa eu lacus sodales libero maecenas massa: est a phasellus.

Dolor nullam, at velit curae vitae netus himenaeos nisi. Semper blandit torquent duis blandit orci himenaeos vehicula facilisis dignissim class. Diam sapien cum justo torquent fusce pulvinar tellus. Ante venenatis inceptos hac diam auctor sodales. Feugiat iaculis mauris ut posuere nisl velit hac, cum sed libero: cursus, vehicula viverra ligula tempus suscipit bibendum dui ultrices.

Filling outputs

A card()’s default behavior is optimized for facilitating filling layouts. More specifically, if a fill item (e.g., plotly_widget), appears as a direct child of a card_body(), it resizes to fit the card()s specified height. This means, by specifying height = 250 we’ve effectively shrunk the plot’s height from its default of 400 down to about 200 pixels. And, when expanded to full_screen, the plot grows to match the card()’s new size.

card(
  height = 250,
  full_screen = TRUE,
  card_header("A filling plot"),
  card_body(plotly_widget)
)

A filling plot

Most htmlwidgets (e.g., plotly, leaflet, etc) and some other Shiny output bindings (e.g, plotOutput(), imageOutput(), etc) are fill items by default, so this behavior “just works” in those scenarios. And, in some of these situations, it’s helpful to remove card_body()’s padding, which can be done via spacing & alignment utility classes.

card(
  height = 275,
  full_screen = TRUE,
  card_header("A filling map"),
  card_body(
    class = "p-0",
    leaflet_widget
  ),
  card_footer(
    class = "fs-6",
    "Copyright 2023 RStudio, PBC"
  )
)

A filling map

Copyright 2023 RStudio, PBC

Fill item(s) aren’t limited in how much they grow and shrink, which can be problematic when a card becomes very small. To work around this, consider adding a min_height on the card_body() container. For example, try using the handle on the lower-right portion of this card example to make the card taller/smaller.

This interactive example is a bit contrived in that we’re using CSS resize to demonstrate how to make plots that don’t shrink beyond a certain point, but this concept becomes quite useful when implementing page-level filling layouts (i.e., page_fillable()) with multiple cards.

card(
  height = 300,
  style = "resize:vertical;",
  card_header("Plots that grow but don't shrink"),
  card_body(
    min_height = 250,
    plotly_widget,
    plotly_widget
  )
)

Plots that grow but don't shrink

Troubleshooting fill

As you’ll learn more about in filling layouts, a fill item loses its ability to fill when wrapped in additional UI element that isn’t a fillable container. To fix the situation, use as_fill_carrier() to allow the additional element to carry the potential to fill from the card_body() down to the fill item.

Multiple card_body()

A card() can have multiple card_body()s, which is especially useful for:

1. Combining both resizable and non-resizable contents (i.e., fill items and non-fill).
2. Allowing each card_body() to have their own styling (via inline styles and/or utility classes) and resizing limits (e.g., min_height).

For example, when pairing filling output with scrolling content, you may want min_height on the filling output since the scrolling content will force it to shrink:

card(
  height = 375,
  full_screen = TRUE,
  card_header(
    "Filling plot, scrolling description"
  ),
  card_body(
    min_height = 200,
    plotly_widget
  ),
  card_body(
    class = "lead container",
    lorem::ipsum(paragraphs = 10, sentences = 5)
  )
)

Filling plot, scrolling description

Lorem tempor, fusce porttitor posuere proin, magna himenaeos? Tristique volutpat, hendrerit primis eu placerat phasellus senectus felis tempor, blandit fringilla pellentesque? Condimentum urna dui per nibh, cum mi a dignissim? Iaculis turpis cras nullam vestibulum, nullam sem mi. Laoreet egestas nulla cras.

Amet tortor metus purus phasellus, habitasse, taciti torquent proin sed. Nam tellus eget pharetra est, varius pretium ridiculus velit mattis placerat morbi. Etiam turpis sagittis, elementum faucibus; vivamus lacus. Metus tellus rutrum placerat orci enim leo mus odio accumsan. Blandit non, urna a quam, integer; diam massa urna suscipit sollicitudin.

Consectetur pharetra a placerat sagittis eu donec fringilla laoreet. Nullam hac in tincidunt ad senectus nec torquent? Platea justo laoreet cras aliquet praesent massa sed. Ad posuere quam aliquam donec tortor cursus aptent – venenatis urna, vivamus feugiat. Nibh elementum phasellus imperdiet volutpat blandit magnis sem viverra, velit platea pretium porttitor ad.

Amet convallis himenaeos montes nostra bibendum senectus cubilia, pulvinar etiam ante himenaeos inceptos donec cubilia. Rutrum facilisis luctus morbi metus, faucibus senectus taciti ridiculus nibh mollis varius faucibus. Tristique ultrices nulla aliquet, suscipit – maecenas eu enim lectus dis nunc orci ultrices etiam. Pretium platea ut semper urna rutrum eget. Enim.

Ipsum vestibulum magna tortor suspendisse fringilla nullam eu! Malesuada egestas in faucibus, cum cursus, rhoncus egestas non. Fusce cursus fames fermentum, posuere, tincidunt montes augue ac sagittis. Sagittis vitae lobortis purus ac: primis dignissim eget ut, ante, tempus porta quis. Purus suscipit litora nullam lectus posuere varius, nisi conubia quam – maecenas curabitur erat penatibus; dictum odio.

Amet velit curae orci luctus, non, aptent sapien litora dictum! Congue feugiat ut odio ullamcorper ad, sed ridiculus aptent cubilia! Libero malesuada facilisis justo odio elementum ligula faucibus tempor fringilla. Diam etiam montes tincidunt: nostra litora ultrices eleifend? Fusce a ut nibh egestas semper purus.

Sit dapibus viverra morbi odio elementum primis lobortis iaculis cubilia mollis. Libero mattis auctor, urna aliquam placerat magnis primis. Quisque in id dignissim fusce; consequat ante rutrum dictumst donec! Dictum porta eget tincidunt, non dis. Nibh curabitur habitant malesuada sed vehicula sagittis porttitor molestie risus magna penatibus.

Elit ut sagittis pharetra cum penatibus fringilla enim, ut pulvinar quis condimentum facilisi dictum laoreet. Orci pharetra tortor ultrices at duis potenti ac magnis, mi sodales, felis cum nisi interdum ornare. Tristique nisl cursus elementum potenti, quisque curae felis dapibus. Arcu mattis nibh, elementum purus sed bibendum vehicula inceptos. Quis pretium habitant suscipit etiam proin sem fermentum, erat condimentum, cum cum sed massa nascetur!

Lorem venenatis vehicula vestibulum taciti lacus praesent eros himenaeos egestas suscipit! Himenaeos condimentum penatibus lacinia bibendum egestas cum natoque, sociosqu enim leo in. Molestie ornare hendrerit senectus lectus orci id – elementum, accumsan erat porttitor! Praesent donec – quisque tellus vivamus eleifend tortor primis. Dapibus blandit nisl molestie eu massa accumsan?

Consectetur ligula cursus interdum et suscipit, suscipit phasellus facilisi elementum. Dui parturient dignissim lobortis tempus nibh fusce nam, nullam ultricies, id augue. Habitant eleifend auctor sem justo, donec parturient nunc cursus sollicitudin per phasellus. Quis tristique diam faucibus, cursus felis rhoncus! Accumsan suscipit ac integer rhoncus torquent: potenti nisi commodo euismod.

Also, when the content has a fixed size, and should not be allowed to scroll, set fill = FALSE:

card(
  height = 350,
  full_screen = TRUE,
  card_header(
    "Filling plot, short description"
  ),
  plotly_widget,
  card_body(
    fill = FALSE,
    card_title("A subtitle"),
    p(class = "text-muted", "And a caption")
  )
)

Filling plot, short description

A subtitle

And a caption

Multiple columns

As you’ll learn in column-based layouts, layout_column_wrap() is great for multi-column layouts that are responsive and accommodate for filling output. Here we have an equal-width 2-column layout using width = 1/2, but it’s also possible to have varying column widths.

card(
  height = 350,
  full_screen = TRUE,
  card_header("A multi-column filling layout"),
  card_body(
    min_height = 200,
    layout_column_wrap(
      width = 1/2,
      plotOutput("p1"),
      plotOutput("p2")
    )
  ),
  lorem::ipsum(paragraphs = 3, sentences = 5)
)

A multi-column filling layout

Sit pulvinar penatibus: litora scelerisque nec etiam, pellentesque, interdum mi taciti. Neque ac molestie mattis imperdiet tortor hac lacus facilisi! Aenean nisl velit, odio; nisl primis vestibulum inceptos nisi ullamcorper etiam magna? Neque tincidunt, dictumst nullam in lacinia malesuada fringilla tortor! Ridiculus ullamcorper fermentum vehicula habitasse nulla gravida, duis suspendisse ultrices!

Ipsum habitant dignissim platea fermentum aptent volutpat. Ullamcorper mus diam primis ante integer proin – urna bibendum suspendisse eleifend diam. Risus aenean eget, conubia viverra primis leo etiam ante nostra habitant. Consequat accumsan habitant suspendisse hendrerit tortor etiam nisl class nam? Quam pulvinar auctor mus penatibus himenaeos, lectus senectus hac odio augue arcu sapien fusce, sollicitudin massa vulputate auctor.

Elit torquent habitant consequat eros: torquent erat mus porttitor sociosqu. Habitant molestie mus neque, dictumst ac sagittis vestibulum bibendum. Neque lectus habitant quam dictum taciti vulputate justo duis quis fames. Taciti proin donec orci interdum gravida nibh, pretium pellentesque proin auctor habitant metus? Curabitur!

Multiple cards

layout_column_wrap() is especially nice for laying out multiple cards since each card in a particular row will have the same height (by default). Learn more in column-based layouts.

layout_column_wrap(
  width = 1/2,
  height = 300,
  card(full_screen = TRUE, card_header("A filling plot"), plotly_widget),
  card(full_screen = TRUE, card_header("A filling map"), card_body(class = "p-0", leaflet_widget))
)

A filling plot

A filling map

Multiple tabs

navset_card_tab() and navset_card_pill() make it possible to create cards with multiple tabs or pills. These functions have the same full_screen capabilities as normal card()s as well some other options like title (since there is no natural place for a card_header() to be used). Note that, each nav_panel() object is similar to a card(). That is, if the direct children aren’t already card items (e.g., card_title()), they get implicitly wrapped in a card_body().

library(leaflet)
navset_card_tab(
  height = 450,
  full_screen = TRUE,
  title = "HTML Widgets",
  nav_panel(
    "Plotly",
    card_title("A plotly plot"),
    plotly_widget
  ),
  nav_panel(
    "Leaflet",
    card_title("A leaflet plot"),
    leaflet_widget
  ),
  nav_panel(
    shiny::icon("circle-info"),
    markdown("Learn more about [htmlwidgets](http://www.htmlwidgets.org/)")
  )
)

HTML Widgets

• Plotly
• Leaflet

A plotly plot

A leaflet plot

Learn more about htmlwidgets

Sidebars

As you’ll learn more about in sidebar layouts, layout_sidebar() just works when placed inside in a card(). In this case, if you want fill items (e.g., plotly_widget) to still fill the card like we’ve seen before, you’ll need to set fillable = TRUE in layout_sidebar().

card(
  height = 300,
  full_screen = TRUE,
  card_header("A sidebar layout inside a card"),
  layout_sidebar(
    fillable = TRUE,
    sidebar = sidebar(
      actionButton("btn", "A button")
    ),
    plotly_widget
  )
)

A sidebar layout inside a card

A button

Static images

card_image() makes it easy to embed static (i.e., pre-generated) images into a card. Provide a URL to href to make it clickable. In the case of multiple card_image()s, consider laying them out in multiple cards with layout_column_wrap() to produce a grid of clickable thumbnails.

card(
  height = 300,
  full_screen = TRUE,
  card_image(
    file = "shiny-hex.svg",
    href = "https://github.com/rstudio/shiny"
  ),
  card_body(
    fill = FALSE,
    card_title("Shiny for R"),
    p(
      class = "fw-light text-muted",
      "Brought to you by RStudio."
    )
  )
)

Shiny for R

Brought to you by RStudio.

Flexbox

Both card() and card_body() default to fillable = TRUE (that is, they are CSS flexbox containers), which works wonders for facilitating filling outputs, but it also leads to surprising behavior with inline tags (e.g., actionButton(), span(), strings, etc). Specifically, each inline tag is placed on a new line, but in a “normal” layout flow (fillable = FALSE), inline tags render inline.

card(
  card_body(
    fillable = TRUE,
    "Here's some", tags$i("inline"), "text",
    actionButton("btn1", "A button")
  ),
  card_body(
    fillable = FALSE,
    "Here's some", tags$i("inline"), "text",
    actionButton("btn2", "A button")
  )
)

Here's some inline text A button

Here's some inline text A button

That said, sometimes working in a flexbox layout is quite useful, even when working with inline tags. Here we leverage flexbox’s gap property to control the spacing between a plot, a (full-width) button, and paragraph. Note that, by using markdown() for the paragraph, it wraps the results in a <p> tag, which means the contents of the paragraph are not longer subject to flexbox layout. If we wanted, we could do something similar to render the actionButton() inline by wrapping it in a div().

card(
  height = 325, full_screen = TRUE,
  card_header("A plot with an action links"),
  card_body(
    class = "gap-2 container",
    plotly_widget,
    actionButton(
      "go_btn", "Action button",
      class = "btn-primary rounded-0"
    ),
    markdown("Here's a _simple_ [hyperlink](https://www.google.com/).")
  )
)

A plot with an action links

Action button

Here's a simple hyperlink.

In addition to gap, flexbox has really nice ways of handling otherwise difficult spacing and alignment issues. And, thanks to Bootstrap’s flex utility classes, we can easily opt-in and customize defaults.

card(
  height = 300, full_screen = TRUE,
  card_header(
    class = "d-flex justify-content-between",
    "Centered plot",
    checkboxInput("check", " Check me", TRUE)
  ),
  card_body(
    class = "align-items-center",
    plotOutput("id", width = "75%")
  )
)

Centered plot

Check me

Shiny

Since this article is statically rendered, the examples here use statically rendered content/widgets, but the same card() functionality works for dynamically rendered content via Shiny (e.g., plotOutput(), plotlyOutput(), etc).

An additional benefit that comes with using shiny is the ability to use getCurrentOutputInfo() to render new/different content when the output container becomes large enough, which is particularly useful with card(full_screen = T, ...). For example, you may want additional captions/labels when a plot is large, additional controls on a table, etc (see the value boxes article for a clever use of this).

# UI logic
ui <- page_fluid(
  card(
    max_height = 200,
    full_screen = TRUE,
    card_header("A dynamically rendered plot"),
    plotOutput("plot_id")
  )
)

# Server logic
server <- function(input, output, session) {
  output$plot_id <- renderPlot({
    info <- getCurrentOutputInfo()
    if (info$height() > 600) {
      # code for "large" plot
    } else {
      # code for "small" plot
    }
  })
}

shinyApp(ui, server)

Appendix

The following CSS is used to give plotOutput() a background color; it’s necessary here because this documentation page is not actually hooked up to a Shiny app, so we can’t show a real plot.

.shiny-plot-output {
  background-color: #216B7288;
  height: 400px;
  width: 100%;
}